1. Field of the Invention
Catalytic converters are used to clean the exhaust gases of internal combustion engines. The efficiency of the catalytic converter determines the quality of the exhaust gas. Aging and poisoning, however, lessens the conversion capacity of the catalytic converter.
To meet legal limit values, it is necessary to ascertain the efficiency of the catalytic converter on an ongoing basis and to output a signal if the efficiency and hence the conversion capacity of the catalytic converter drops below a predetermined threshold, the result of which is that the exhaust gas leaving the catalytic converter does not meet the legal requirements.
2. Description of the Related Art
There has become known heretofore from European patent disclosure EP 0 444 783 A1 a method for monitoring the conversion capacity of the catalytic converter , in which an oxy g e n sensor that measures the oxygen concentration in the exhaust gas is provided at the outlet of the catalytic converter. In lambda control, the air/fuel ratio delivered to the engine is adjusted so that it oscillates around the lambda value of 1. In accordance with the lambda control, the oxygen sensor measures an oscillating oxygen concentration at the outlet of the catalytic converter. The difference between the maximum and minimum values of the oscillating oxygen concentration is used as a criterion for the conversion capacity of the catalytic converter, which is greater the less the distance between the maximum value and the minimum value.
That prior art method is relatively imprecise.